why do some blackjack games restrict doubles on 11 only

never got why some places only let you double down on 11. seems like they’re just trying to squash any chance you have to get creative with the basic strategy. i get that doubling on 11 has the highest expected value, but letting players double on 9 or 10 can create more edge if the dealer’s showing a weak card. maybe the house figures most people double wrong anyway so they limit it just to 11, less risk for them.

in poker, the rules flex a little to keep things flowing, but blackjack feels like every shift just goes against players over time, especially with these rules changes. maybe it’s to speed up the game or protect against counters? or just more revenue in the margins? anyone see actual numbers on how much it shifts the house edge?